The present invention relates to an automatic sewing machine wherein a stitch path is controlled automatically by varying a relative position between a needle and a workpiece;
In this type of conventional automatic sewing machine, the relative position between the needle and the workpiece is varied in such a manner that the workpiece is moved relative to the reciprocal path of the needle in respect of a horizontal direction, or the reciprocal path of the needle is moved relative to the workpiece fixed in respect of the horizontal direction. Generally, for the purpose of forming stitch pattern which has two-dimensional shape, it is required to vary the position of the workpiece relative to the reciprocal path of the needle in biaxial directions in a horizontal plane. In the conventional automatic sewing machine as disclosed in U.S. Pat. Nos. 4,513,677, 3,552,336 and 3,713,406, for example, a first moving means (X-direction moving means, for example) for moving the sewing head or the workpiece and a second moving means (Y-direction moving means, for example) are arranged at right angles in such a manner that the X-direction moving means is mounted on the Y-direction moving means. Thus, the movement of the sewing head or the workpiece in the Y-direction is effected by the Y-direction moving means, and the movement of the sewing head or the workpiece in the X-direction is effected by the X-direction moving means on the Y-direction moving means. Accordingly, the structure of the X-direction and Y-direction moving means is complicated. Further, the mass to be moved by the Y-direction moving means includes not only the mass of the sewing head or the workpiece clamping means but also the mass of the X-direction moving means, causing an increased inertia. To cope with this increased inertia, it is necessary to make a response speed large and therefore to provide a large driving means. In addition, as both the moving means are cooperatively connected, vibration or deflection generated in the Y-direction moving means directly affects a positioning accuracy in the X-direction.
Some of the conventional automatic sewing machine have a preparing area for preparing a workpiece prior to a sewing operation and a sewing area where the sewing operation is carried out. In this type of sewing machine the workpiece prepared in the preparing area is required to be transferred to the sewing area. Accordingly, it is required to provide a workpiece transferring means in addition to the moving means for varying the relative position between the needle and the workpiece during the sewing operation. There is disclosed this type sewing machine having a mechanism serving as both the workpiece transferring means and the moving means during the sewing operation in U.S. Pat. No. 3,528,378. In this type of sewing machine, the moving means for varying the relative position between the needle and the workpiece is required to have a length in at least X- or Y-direction enough to transfer the workpiece from the preparing area to the sewing area. Accordingly, the moving means extending from the preparing area to the sewing area is long and tends to be vibrated or deflected. The vibration or deflection in one-direction moving means causes bad influence to the other-direction moving means thereon to make the stitch pattern inaccurate. To cope With this problem, the automatic sewing machine is rendered larger and more complicated.